Electrooptical devices, electrooptical thin crystal films and methods making same

ABSTRACT

A method of fabrication of an electrooptical device comprises depositing a colloid system of anisometric particles onto at least one electrode and/or onto at least one substrate and/or onto at least one layer of an isotropic or anisotropic material to form at least one layer of an electrooptical material, externally aligning the colloid system to form a preferred alignment of the colloid system particles, drying the colloid system, and forming at least one electrode and/or at least one layer of an isotropic or anisotropic material on at least a portion of the layer of the electrooptical material.

FIELD OF THE INVENTION

This invention relates in general to electrooptical devices, andparticularly to electrooptical devices capable of controlling radiationin the visible and near IR range.

BACKGROUND OF THE INVENTION

Electrooptical devices based on electrooptical materials such as lithiumniobate (LiNbO₃), KDP and KTP have been hereto described. See I. P.Kaminov et al., “Optical Fiber Telecommunications”, Vol. IIIB, Ed. byAcademic Press (1997).

There are known electrooptical devices such as light modulators based ona D-shaped optical fiber and using a lithium niobate crystal. See W.Johnstone et al., “Fiber Optic Modulators Using Active MultimodeWaveguide Overlays”, Electron. Lett., Vol. 27, No. 11, 894-896 (1991).D-shaped optical fiber, also called side-polished optical fiber, refersto an optical fiber having a D-shaped cross section. Light modulators ofthis type are usually produced on a plane-parallel plate of a quartzglass which is provided with a groove having a curvature typically fromseveral dozens of centimeters to several meters. A single-mode ormonomode optical fiber is glued into this groove. Then the plate sidehaving the groove with the fiber glued therein is ground until thisplane reaches the fiber core so that the fundamental mode (localizedpredominantly in the core) can penetrate through the reflective claddingto the polished surface. After this processing, the optical fibersection becomes D-shaped. See S. M. Tseng et al., “Side-PolishedFibers”, Appl. Optics, Vol. 31, No. 18, 3438-3447 (1992). The polishedsurface of the D-shaped optical fiber is coated with a thin transparentelectrode layer of indium tin oxide (ITO) composition. Then a thinlithium niobate crystal is glued onto this electrode and ground toreduce the thickness to 20-30 microns. Finally, the second electrode isapplied above the lithium niobate crystal layer.

The light modulator operates as follows. An external voltage applied tothe electrooptical lithium niobate crystal changes the refractive indexof the material and modifies the condition of resonance between thefundamental mode of the optical fiber and the guided modes of thelithium niobate layer. The resonance condition is essentially thecondition of phase synchronism, or equal propagation constants of theguided modes of the planar optical waveguide with a lithium niobate coreand the fundamental mode of the D-shaped optical fiber. When the modesare in resonance, the light signal is effectively pumped from theoptical fiber into the lithium niobate crystal and the output signalintensity at the fiber end is decreased. If the applied voltage ischanged so as to alter the refractive index of the lithium niobatecrystal and break the resonance, the light passes through the D-shapedoptical fiber without loss in intensity. In the prior art, a significantlevel of the output signal modulation is achieved by applying a voltageof 150 V to a 35 micron-thick control layer between ITO electrodes.

One disadvantage of the light modulator described above is that themanufacturing process for thin lithium niobate layers is verycomplicated. Further, the interelectrode distance determined by thethickness of the lithium niobate crystal is relatively large.

Optical switches using the same principle of operation have beendescribed employing a layer of material with variable refractive indexon the surface of a D-shaped optical fiber and a liquid crystal layer.See S. M. Tseng et al., “Low-Voltage Optical Fiber Switch”, Jpn. J.Appl. Optics, Part 2, Vol. 37, L42-L45 (1998). In the optical switchesof this type, a voltage about 30 V is needed to break the resonance foran interelectrode distance of 13 microns. One disadvantage of thisdevice is the relatively low operation speed determined by the slowresponse of the liquid crystal. The switching time is about 7milliseconds and the liquid crystal cannot be reoriented by an acvoltage with a frequency of 100 Hz.

There are known electrooptical devices such as light modulators havingcharge carrier injectors. See E. R. Mustel et al., “Light Modulation andScanning Methods”, Nauka, Moscow (1970). The light modulator of thistype employs a layer of an electrooptical material representing ann-type semiconductor film on a substrate. The light propagates alongthis film which serves as the optical waveguide. Deposited above thisn-type film is a layer of a p-type semiconductor, which forms a p-njunction. The device also contains a pair of electrodes, one in ohmiccontact with the n-type semiconductor film and the other with the p-typesemiconductor film, to which a control (dc or ac) voltage is applied.When a control voltage is applied to the p-n junction in the forwarddirection, the charge carriers (holes) are injected into the opticalwaveguide (n-type semiconductor film). The injection of holes into theoptical waveguide increases the optical absorption of the material, thusmodulating the light.

One disadvantage of this type of light modulators is the current-inducedheating of the p-n junction, which requires taking special measures tothermally stabilize the entire device. Another disadvantage is thelimitation imposed on the modulation frequency by the mechanism of lightmodulation employed in this device. Indeed, the lifetime of the minoritycarriers injected through the p-n junction is limited, usually to about10⁻⁶ seconds for the holes. For this reason, the light modulators guidedby the minority carrier injection can operate only at frequencies up to10⁵-10⁶ Hz. The electric current passed through the optical waveguidemust be of sufficiently large density. This requirement poseslimitations on the system dimensions. The greater the size of thedevice, the higher the current required to maintain the density on alevel necessary for the device operation. A further disadvantage relatedto the electric current passage is the large energy consumption, whichincreases with the current value.

There are known electrooptical devices which contain a layer of amaterial whose optical properties change depending on the appliedelectric field strength. See WO 00/45202. One example of such materialis ferroelectric ceramics. Ceramic materials possessing ferroelectricproperties usually exhibit the phenomenon of birefringence. Thus, theceramic layer is an electrooptical material and the applied electricfield can control the device. Owing to a combination of theferroelectric and electrooptical properties of the material, this systemcan be employed for controlling and modulating light signals in fiberoptic communication systems, nonlinear optical devices, andelectrooptical devices such as modulators, shutters, and frequencymultipliers, etc.

The observed optical effects are related to orientation or reorientationof the domain polarization vector in an applied electric field. As aresult, the optical axes of the ceramic grains are oriented orreoriented as well. The reorientation of domains in the electroopticalceramic material under the action of an applied electric field isaccompanied by the development of mechanical stresses perpendicular tothe field direction.

One disadvantage of the ferroelectric ceramics is that they retainorientation of the domain polarization vector for an arbitrarily longtime after switching off the film. Therefore, additional measures haveto be taken in order to restore the initial state, such as applyingcontrol pulses with opposite polarity and half amplitude, mechanicallydeforming the ceramic substrate, and applying a high-frequency electricfield of small amplitude. This property of the ferroelectric ceramicscomplicates the control system of the electrooptical devices.

Another disadvantage of the ferroelectric ceramics is the difficulty ofensuring a fast operation speed. Indeed, an increase in the lightmodulation rate at a given modulation efficiency requires increasing thecontrol voltage amplitude. This fact and the delayed electroopticalresponse in such materials are related to the energy consumption for theformation and reorientation of the domain walls. For example, atelectric pulse duration of about 2 μs, the pulse amplitude must be twotimes greater than the quasistatic control voltage; to reduce the pulseduration to 1 μs, the pulse amplitude must be three times greater, andso on.

Additional disadvantage is the fatigue inherent in the ferroelectricceramic materials. Straining a ceramic material in the rangecorresponding to the spatial modulation of light (e.g., at the expenseof partial repolarization) encounters difficulties related to thedeformation character of the field-induced polarization. For thisreason, repeated on-off cycles of an electric field, especially of largestrength (above 5 kV/cm), lead to the accumulation of a residualdeformation. This residual deformation decreases the optical contrast ofmodulated light, which is manifested by irreversible polarization of theelectrooptical ferroelectric ceramic layer.

Another disadvantage of the above device is extremely strong temperaturedependence of the characteristics of a ferroelectric layer. Temperaturevariations lead to changes in the optical properties of the controldevice. In order to exclude the temperature drift, it is necessary toprovide the control device with a thermal stabilization system, whichincreases the energy consumption, complicates the device, and increasesthe cost of production.

A significant disadvantage of the device employing ferroelectricceramics is the probability of phase distortions introduced into thedata processed as a result of strong deformation of the ceramic plateand the inverse piezoelectric effect. The presence of defects andinternal stresses leads to degradation of the properties of suchmaterials which are extremely sensitive to manufacturing processparameters, making production of the devices a difficult task.

There are known electrooptical devices based on organic materials. SeeU.S. Pat. No. 5,172,385 to Forrest et al. and L. M. Blinov, “Electro-and Magneto-optics of Liquid Crystals”, Nauka, Moscow (1978), pp. 115,351, 352. The devices of this type contains two electrodes which areeither both transparent if the system operates in the beam transmissionmode, or transparent and reflecting, if the system operates in the beamreflection mode. An electrooptical material layer placed between theelectrodes represents a liquid crystal, the thickness of which(interelectrode distance) is determined by sealing spacers. Theelectrodes are deposited onto glass substrates.

A large number of the chemical classes of organic molecules provides fora broad spectrum of materials which can be effectively used in fiberoptics, integrated optics, and optical communications.

There are classes and groups of organic substances of various chemicalnatures, composed of the molecules or molecular chains such asphthalocyanines, polyacetylenes, aromatic hydrocarbons, conjugatedpolymeric systems, etc. that possess dielectric, semiconducting, andeven metallic properties. A common feature of these molecules is thepresence of superstructures. There are known organic films based onpolymeric materials (U.S. Pat. Nos. 4,204,216; 4,663,001; 4,269,738;5,104,580; 3,775,177; F.R. Patent No. 2,583,222), salts of linearpolyaniline compounds (U.S. Pat. No. 4,025,704), phthalocyaninederivatives (U.S. Pat. Nos. 5,525,811; 6,051,702), organic dyes (U.S.Pat. No. 3,844,843), and porphyrins (U.S. Pat. Nos. 3,992,205;3,935,031), which are widely used in modern electronic devices as thelayers generating charge carriers in the course of photoelectronprocesses in photovoltaic devices (U.S. Pat. No. 4,164,431), solar cells(U.S. Pat. No. 3,844,843), and polarization devices (U.S. Pat. No.5,172,385).

There are various known methods for the formation of organic films andcreation of anisotropic film structures, for example Langmuir-Blodgetttechnique (U.S. Pat. No. 5,079,595), molecular beam epitaxy, etc.However, optical devices employing liquid-crystalline molecularcompounds possess a number of disadvantages, in particular, requirespecially prepared substrates, alignment layers, or high-vacuumconditions for the obtaining of highly ordered and clean structures.Special and advanced technologies are employed and even these oftencannot ensure the obtaining of films possessing a certain type of orderand ensuring required optical anisotropy.

There are known electrooptical devices using an electrooptical materialof a liquid crystal (host) matrix with dispersed organic dye (guest)molecules. See I. K. Vereshchagin et al., “Introduction toOptoelectronics”, p. 173, Vysshaya Shkola, Moscow (1991), L. M. Blinovet al., “Electrooptical Effects in Liquid Crystal Materials”, p. 182,Springer-Verlag, New York (1994). The control device operates on theguest-host interaction principle and is structurally analogous to thatdescribed above, comprising two electrodes which are either bothtransparent if the system operates in the beam transmission mode, ortransparent and reflecting, if the system operates in the beamreflection mode. An electrooptical material layer placed between theelectrodes represents a liquid crystal doped with dye molecules. Thethickness of this layer (interelectrode distance) is determined bysealing spacers placed between the electrodes deposited onto glasssubstrates. The molecules of liquid crystal and dye are oriented in thesame direction parallel to the alignment layers. In the absence of anapplied voltage, a light polarized in the long axis of dye molecules isabsorbed and no signal is transmitted through the optical device. Thisabsorption in the dye is related to the fact that the electric field ofthe light polarized parallel to the long axis of the dye moleculesdrives electrons to oscillate between the ends of the molecule, thusconsuming the beam energy. An external voltage applied to the electrodescreates an electric field in the liquid crystal. This field rotates theliquid crystal molecules and, hence, the dye molecules (due to theguest-host effect) so that the long axis of the dye molecules becomesperpendicular to the plane of polarization of the light beam. In thiscease, electrons in the dye molecules are not forced to move by theelectric field of the light beam. Therefore, the light is not absorbedin the liquid crystal layer and the beam is transmitted through theoptical device without significant losses.

One disadvantage of the above optical device is the relatively lowoperation speed of, which is characterized by a switching time on theorder of 0.1 second. This device operates poorly at reducedtemperatures, under which conditions the operation speed further sharplyreduces. The device has insufficient working life, which amounts toabout 10⁴ hours.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anelectrooptical device that eliminates the disadvantages inherent in theknown devices described above.

Another object of the present invention is to provide an electroopticaldevice that uses considerably low working voltages.

A further object of the present invention is to provide anelectrooptical device that can control both polarized and non-polarizedlight waves.

An additional object of the present invention is to provide anelectrooptical device that creates voltage-controlled active devices forfiltration, commutation, and modulation of optical signals.

A still further object of the present invention is to provide alow-cost, material-and-energy-saving method for producing electroopticaldevices.

Another object of the present invention is to provide a method ofcontrolling the thickness of an electrooptical anisotropic thin crystalfilm based on the net solid phase content in the liquid crystal phaseand the thickness of an applied wet layer.

A further object of the present invention is to provide anelectrooptical device that can obtain electrooptical effects withoutpassing electric current through the layer of an electroopticalmaterial.

A further object of the present invention is to provide a small-sizeelectrooptical device based on optical fibers for fiber opticcommunication.

A further object of the present invention is to provide anelectrooptical device with refractive index depending on the strength ofan applied electric field or the electric field of a light wave.

A still further object of the present invention is to provide anelectrooptical device with the optical absorption band shifted under theaction of an applied electric field.

These and other objects of the present invention are achieved by thepresent electroooptical device and the method making the device. Theelectrooptical device of the present invention comprises at least onesubstrate, at least one pair of electrodes and at least one layer of anelectrooptical material. The electrooptical material represents anoptically anisotropic thin crystal film and contains molecules havingaromatic rings and possessing a lattice with an interplanar spacing(Bragg's reflection) of 3.4±0.2 Å along one of optical axes. Theelectrooptical material has anisotropic refractive indices and/oranisotropic absorption coefficients that are depended on an electricfield strength.

In another embodiment, the present invention provides a method offabricating an electrooptical device. According to the present method, acolloid system of anisometric particles is deposited onto at least oneelectrode and/or onto at least one substrate and/or onto at least onelayer of an isotropic or anisotropic material to form at least one layerof an electrooptical material. An external alignment action is appliedto the colloid system to form a preferred alignment of the colloidsystem particles. The colloid system is then dried. At least oneelectrode and/or at least one layer of an isotropic or anisotropicmaterial is then formed on at least a portion of the layer of theelectrooptical material.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from the followingdescription when read in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic illustrating an electrooptical device inaccordance with one embodiment of the present invention.

FIG. 2 is a schematic illustrating an electrooptical device containing anontransparent electrode in accordance with one embodiment of thepresent invention.

FIG. 3 is a schematic illustrating an electrooptical device containing aprotective layer formed between an upper electrode and an opticallyanisotropic thin crystal film in accordance with one embodiment of thepresent invention.

FIG. 4 is a schematic illustrating an electrooptical device representinga light modulator with a toroidal cavity in accordance with oneembodiment of the present invention.

FIG. 5 is a schematic illustrating an electrooptical device in which alight beam propagates in an electrooptical anisotropic thin crystal filmin the direction parallel to an applied electric field, in accordancewith one embodiment of the present invention.

FIG. 6 is a schematic illustrating an electrooptical device in whichelectrodes partially extend to one surface of the electroopticalmaterial layer in accordance with one embodiment of the presentinvention.

FIG. 7 is a schematic illustrating an electrooptical device representinga multilayer modulator cell in accordance with one embodiment of thepresent invention.

FIG. 8 is a schematic illustrating an electrooptical device in which thesubstrate represents an optical fiber with core and reflective cladding,in accordance with one embodiment of the present invention.

FIG. 9 is a schematic illustrating an electrooptical device in which theactive (voltage-controlled) system of two cylindrical electrodes andelectrooptical layers is formed in two regions on the optical fiber, inaccordance with one embodiment of the present invention.

FIG. 10 is a schematic illustrating an electrooptical device in whichthe cylindrical electrooptical material layer is formed on the surfaceof the reflective cladding of an optical fiber, in accordance with oneembodiment of the present invention.

FIG. 11 is a schematic illustrating an electrooptical device in whichthe active (voltage-controlled) system of two electrodes andelectrooptical layer is formed on a flat surface of the reflectivecladding of a D-shaped optical fiber, in accordance with one embodimentof the present invention.

FIG. 12 is a schematic illustrating an electrooptical device in whichthe active (voltage-controlled) system of two electrodes andelectrooptical layer is formed in a region of “waist” of the opticalfiber, in accordance with one embodiment of the present invention.

FIG. 13 is a schematic illustrating an electrooptical device in whichthe active (voltage-controlled) system of two electrodes andelectrooptical layer is formed on a flat end surface of a fiber with thecore and the reflective cladding, in accordance with one embodiment ofthe present invention.

FIG. 14 is schematic illustrating a guided electrooptical device basedon an optical fiber with oblique end surface.

FIG. 15 is a schematic illustrating an electrooptical device operatingon the same principle as in FIG. 14, in accordance with one embodimentof the present invention.

FIG. 16 is a schematic illustrating an electrooptical device based on anoptical fiber with a long-period grating formed in the fiber core, inaccordance with one embodiment of the present invention.

FIG. 17 is a schematic illustrating an electrooptical device having twolong-period gratings formed in the fiber core and an active system ofelectrodes and electrooptical layer formed in the region between the twogratings on the surface of reflective cladding of the fiber, inaccordance with one embodiment of the present invention.

FIG. 18 is a schematic illustrating an electrooptical device combiningthe features of the devices depicted in FIGS. 16 and 17, in accordancewith one embodiment of the present invention.

FIG. 19 is a schematic illustrating an electrooptical device employingthe Bragg grating formed in the layer of an electrooptical material bycreating the corresponding profile of the refractive index, inaccordance with one embodiment of the present invention.

FIG. 20 is a schematic illustrating an electrooptical device comprisingtwo single-mode D-shaped optical fibers with the cores and thereflective claddings, which are rotated with their flat polishedsurfaces toward each other, in accordance with one embodiment of thepresent invention.

FIG. 21 is a schematic illustrating an electrooptical device, comprisingtwo single-mode D-shaped optical fibers rotated with their flat polishedsurfaces toward each other, in accordance with one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

In general, the present invention provides an electrooptical devicecomprising at least one substrate, at least one pair of electrodes andat least one layer of an electrooptical material. The at least one layerof the electrooptical material represents an optically anisotropic thincrystal film and contains molecules having aromatic rings and possessinga lattice with an interplanar spacing (Bragg's reflection) of 3.4±0.2 Åalong one of optical axes, and having anisotropic refractive indicesand/or anisotropic absorption coefficients that are depended on anelectric field strength.

The electrooptical anisotropic thin crystal film of the presentinvention has unique properties including small thickness, lowtemperature sensitivity, high anisotropy of the refractive index,anisotropy of the absorption coefficient, high dichroic ratio, andsimplicity of fabrication. These unique properties are determined by themethod of making the thin crystal film and by the features of thematerial, namely, by a special molecular-crystalline structure obtainedthrough crystallization of a liquid crystal phase, containing at leastone organic compound capable of forming a stable lyotropic orthermotropic liquid-crystalline phase, upon application of the liquidcrystal onto an appropriate substrate, alignment, and drying. Theorganic substance in the present electrooptical anisotropic thin crystalfilm comprises at least one organic compound, the formula of whichincludes (i) at least one ionogenic group ensuring solubility in polarsolvents for obtaining a lyotropic liquid-crystalline phase, and/or (ii)at least one nonionogenic group ensuring solubility in nonpolar solventsfor obtaining a lyotropic liquid-crystalline phase, and/or (iii) atleast one counterion, which may, or may not be retained in the molecularstructure during formation of the material.

The electrooptical anisotropic thin crystal film comprises a greatnumber of supramolecular complexes of one or several organic compoundssuch as those described in J. M. Lehn, “Supramolecular Chemistry:Concepts and Perspectives”, VCH, Weinheim (1995). These supramolecularcomplexes are oriented in a certain manner so as to provide electricconductivity and polarization of the transmitted light.

Selection of the base material for the electrooptical anisotropic thincrystal film is determined by the presence of a developed system ofπ-conjugated bonds in conjugated aromatic rings and by the presence ofgroups such as amine, phenol, ketone, etc. lying in the plane of themolecule and entering into the aromatic system of bonds. The moleculesand/or the molecular fragments possess a planar structure. These can be,for example, organic substances such as indanthrone (Vat Blue 4),1,4,5,8-perylenetetracarboxylic acid dibenzoimidazole (Vat Red 14),3,4,9,10-perylenetetracarboxylic acid dibenzoimidazole, quinacridone(Pigment Violet 19), etc., the derivatives of which (or their mixtures)are capable of forming a stable lyotropic liquid crystal phase.

When dissolved in an appropriate solvent, such organic compound forms acolloidal system (lyotropic liquid crystal) in which molecules areaggregated into supramolecular complexes constituting kinetic units ofthe system, see PCT Publication WO 02/56066. This lyotropic liquidcrystal phase is essentially a precursor of the ordered state of thesystem, from which a solid electrooptical anisotropic thin crystal filmis formed during the subsequent alignment of the supramolecularcomplexes and removal of the solvent.

The present method for making an electrooptical anisotropic thin crystalfilms from a colloidal system with supramolecular complexes includes thefollowing steps:

application of the colloidal system onto a substrate or a device or alayer in a multilayer structure. The colloidal system typicallypossesses thixotropic properties, which are provided by maintaining apreset temperature and a certain concentration of the dispersed phase;

conversion of the applied colloidal system into a high flow state by anyexternal action such as heating, shear straining to reduce viscosity ofthe solution. This action can be applied either during the entiresubsequent alignment stage or lasts for a minimum necessary time, sothat the system does not relax into a state with increased viscosityduring alignment;

external alignment upon the system, which can be produced usingmechanical factors or by any other means, for example by applying anexternal electric field at normal or elevated temperature, with orwithout additional illumination, magnetic field, or optical field (e.g.,coherent photovoltaic effect); the degree of the external alignmentshould be sufficient to impart necessary orientation to the kineticunits of the colloidal system and form a structure, which serves as abase of the crystal lattice of the electrooptical anisotropic thincrystal film;

conversion of the aligned region of the layer from the state of reducedviscosity, which is achieved by the initial action, into a state of theinitial or higher viscosity. This transition is performed so as not tocause disorientation of the electrooptical anisotropic thin crystal filmstructure and not to produce surface defects; and

final drying to remove solvents to form the final electroopticalanisotropic thin crystal film structure.

In the resulting electrooptical anisotropic thin crystal film, themolecular planes are parallel to each other and the molecules form athree-dimensional crystal structure, at least in part of the crystal.Optimization of the production technology may allow the formation of anelectrooptical anisotropic single crystal film. The optical axis in thissingle crystal is perpendicular to the plane of molecules. Such thincrystal films possess a high degree of anisotropy and exhibit, at leastin one direction, a high index of refraction and/or a high absorptioncoefficient.

The optical anisotropy of the present electrooptical anisotropic thincrystal film is described in terms of ellipsoids of the imaginary andreal parts of the complex refractive index characterized in the angularvariation of the absorption coefficient and refractive index,respectively. The components of imaginary (K_(i)) and real (n_(i)) partsof the complex refractive index of the optically anisotropic thincrystal film according to the present invention should simultaneouslymeet the following relations:K₁≧K₂>K₃,(n ₁ +n ₂)/2>n ₃.

where K₁, K₂, K₃ and n₁, n₂, n₃ are the semiaxes of ellipsoids of theimaginary and real parts of the anisotropic complex refractive index ofthe thin crystal film material.

The components of the real and imaginary parts of the anisotropiccomplex refractive index, as well as the directions of the principalaxes of the ellipsoid can be determined by conventional ellipsometricand spectrophotometric techniques.

The required anisotropy of the absorption coefficients (K₁, K₂, K₃) andthe refractive indices (n₁, n₂, n₃), as well as the necessaryorientation of the principal axes (i.e., the optical properties of theelectrooptical anisotropic thin crystal film in a multilayer structure)can be ensured by establishing a certain angular distribution ofmolecules in the polarizing film at the substrate surface.

It is also possible to mix colloidal systems (which leads to theformation of combined supramolecules) so as to obtain a crystal filmpossessing intermediate optical characteristics. In the electroopticalanisotropic thin crystal film obtained from mixed colloidal solutions,the absorption coefficient and refractive index can take various valueswithin the limits determined by the initial components. Such mixing ofdifferent colloidal systems with the formation of combinedsupramolecules is possible due to the coincidence of one characteristicdimension (interplanar spacing of 3.4±0.2 Å) for the organic compoundsemployed.

The thickness of the electrooptical anisotropic thin crystal film isdetermined by the content of solid substance in the applied solution.During formation of such layers, a technological parameter convenientlycontrolled under commercial production conditions is the solutionconcentration.

The degree of crystallinity of the final crystal film can be monitoredby X-ray diffraction and/or by optical methods.

Using the present method, the electrooptical anisotropic thin crystalfilms can be formed on various substrate materials, including metals,semiconductors, dielectrics, crystals, polycrystals, glasses, polymers,and so on. Moreover, the present method allows the electroopticalanisotropic thin crystal films to be obtained on various surfaces ofboth simple (flat) and complicated shapes (cylindrical, conical,spherical, etc.), which allows the present electrooptical anisotropicthin crystal films to be used in electrooptical devices of mostsophisticated design, for example, on the edges and side surfaces ofoptical fibers, on flat polished sides of such fibers, in the internaland external surfaces of the photonic crystal optical fibers (i.e., theoptical fibers containing a system of longitudinal air channels in thecore and/or in the reflective cladding).

Substrates onto which the thin crystal films are applied can beadditionally treated to ensure homogeneous wetting of the surface torender the surface hydrophilic. The possible treatments includemechanical processing, annealing, mechanical-chemical treatment, etc.Prior to application of a thin crystal film, the substrate surface canbe mechanically treated so as to form anisotropic alignment structures,which favors an increase in the degree of molecular order in theobtained thin crystal films.

The possibility of considerably reducing the level of working voltagesis ensured by a small thickness of the anisotropic crystal films on theorder of 100-500 nm, since the electric field strength is determined bythe applied voltage (U) and the film thickness (D) through the formulaE=U/D.

The possibility to create active devices for filtration, control, andcommutation of both polarized and nonpolarized light waves is ensured byusing the material possessing electrical and optical anisotropy with ahigh degree of birefringence: the electrooptical crystal film with athickness of 0.3 micron has a maximum value of Re(n₀−n_(e))=0.85. Withconventional materials, such a birefringence is typically reached at alayer thickness of 200 microns. See P. Lazarev et al., “Thin CrystalFilm Retarders”, Proc. 7th Int. Workshop on Display Materials andComponents, Kobe (Japan), p. 11159-60, Nov. 29-Dec. 1 (2000). Therefractive index of a thin crystal film is determined by the appliedelectric field and can significantly differ from that of the quartzglass substrate. In addition, the thin crystal film material isphotosensitive and changes its optical characteristics under the laserradiation. The refractive index is dependent on the light intensity. Thepresent material possesses interesting nonlinear optical properties.

A low sensitivity of the present electrooptical device with respect totemperature variations is ensured by the thin crystal film possessing ahigh thermal stability as compared to that of conventional materials.The thin crystal film can be thermally treated at temperatures up to180° C. in air or argon for a time period of up to four hours, with aloss in the polarization efficiency not exceeding 0.8%.

High technological properties of the present device are ensured by thata thin crystal film is readily applied onto surfaces of any shape, bothtechnological facilities and the material being relatively cheap. Hightechnological properties of the electrooptical material, simplicity ofthe thin crystal film fabrication, and convenience of the qualitymonitoring favor applications of the present electrooptical anisotropicthin crystal films in fiber optic communication devices such ascontrolled modulators, switches, couplers, attenuators, filters, etc.Using these thin crystal films, it is possible to create miniature fiberoptic devices, since the small-size crystals can be readily formed onthe surface of complicated shape such as the edge or side surface of anoptical fiber. Optical fibers may possess extremely small dimensions bythemselves. Indeed, the core of a single-mode optical fiber has adiameter of 5-10 micron and the reflective cladding diameter amounts to125 micron.

The optical fibers can be made of various materials, including quartzglass, chalcogenide and fluoride glasses, thallium halides and someother inorganic and organic, crystalline and noncrystalline materialssuch as polymers or their combinations. There are three main types ofthe optical fibers: all-glass fibers with both core and reflectivecladding made of glass; glass-plastic systems with glass core andplastic reflective cladding; and all-plastic fibers with both core andreflective cladding made of plastic.

The optical fibers may contain a core and/or one or more reflectivecladdings made of different materials, including quartz glass, fluorideand chalcogenide glasses, thallium halides polycrystalline halides, andpolymers, etc.

Small-size electrooptical anisotropic thin crystals with dimensions fromdozens to hundreds microns can be obtained on all the above fibermaterials. The list of such materials is by no means restricted to theaforementioned examples.

Fabrication of the electrooptical fiber devices of the present inventioninvolves the formation of electrooptical anisotropic thin crystal filmson the surfaces of complicated geometry. The present method allows theelectrooptical anisotropic thin crystal films to be obtained on varioussurfaces including those of both simple (flat) and complicated shape(cylindrical, conical, spherical, etc.). Therefore, the thin crystalfilms can be also formed a cylindrical reflective cladding of an opticalfiber, on a flat oblique fiber end surface, and on a flat polishedsurface of the reflective cladding of a D-shaped fiber (either a curvedfiber ground so that the polished plane is close to the fiber core, or afiber drawn from the blank with a D-shaped cross section and the coresituated close to the flat surface). In particular, the disclosed methodallows a thin crystal films to be obtained on the surface of thereflective cladding of an optical fiber with at least one long-periodgrating formed in the core material. Such gratings can be formed by anysuitable method such as by irradiating or doping the material andprovide for a stronger interaction of a light signal with theelectrooptical anisotropic thin crystal film. Since the applied thincrystal film is photosensitive, both Bragg and long-period gratings canbe recorded in this film as well.

The use of anisotropic thin crystal films in electrooptical devices isbased on the fact that the anisotropic refractive indices and absorptioncoefficients of these materials depend on the applied electric fieldstrength, the film thickness depends on the electric field(electrostriction), and the refractive index depends on the electriccomponent of the optical radiation field. The crystal film, forming anexternal coating on a fiber or planar optical waveguide, interacts witha guided mode capable of penetrating from guiding layers of the opticalwaveguide core into the electrooptical anisotropic thin crystal film.

The electrooptical devices of the present invention will now bedescribed in more detail with reference to FIGS. 1 though 21.

FIG. 1 illustrates an electrooptical device comprising a substrate 1bearing sequentially deposited layers of a first transparent electrode2, electrooptical material representing an anisotropic thin crystal film3, and a second transparent electrode 2. The substrate 1 can be made ofether transparent or nontransparent material including metals,semiconductors, and dielectrics. Preferably the substrate 1 is made ofglass, quartz, or plastic. The transparent electrodes 2 can be made oftin oxide (SnO₂) or indium oxide (In₂O₃). The layers of SnO₂ with aresistivity of 300 Ohm/cm² and below are obtained by pyrolysis of SnCl₄or hydrated SnCl₂ in a muffle furnace at 400-500° C. This technique canbe used for depositing an electrode layer on a substrate prior toapplication of an anisotropic thin crystal film. The electrode layerscan be either thin or thick, depending on the application requirementssuch as transparency and low electric resistance. The SnO₂ layers can besoldered to thin metal conductors using a dilute ethanol solution ofBF-2 or BF-4 glue as a flux. The layers of indium oxide are obtained bycathode sputtering in a vacuum of 10⁻⁵ Torr. Cathode sputtering is moretechnologically advanced and can produce indium oxide films havingapproximately the same properties (mechanical strength, opticaltransmission, resistivity) as those of SnO₂ films. If a transparentconducting electrode film is used on a glass substrate, it is alsopossible to use Cu₂S layers. Electrodes are connected to a source of dcand/or ac bias voltage.

FIG. 2 illustrates an electrooptical device which further comprises anontransparent electrode 4. This nontransparent electrode can be formedon the surface of the optically anisotropic thin crystal film byspraying a metal such as aluminum in vacuum. Other candidate materialsfor nontransparent electrodes are gold, titanium, etc. The lighttransmission through the system is provided by windows, which areformed, for example, by depositing a metal electrode through a mask orby any other means.

FIG. 3 illustrates an electrooptical device in which an additionalprotective layer 5 is provided between the upper electrode 4 and theoptically anisotropic thin crystal film 3. This protective layer 5prevents mutual diffusion of the substances of the electrode andanisotropic electrooptical material. In the case of an aluminumelectrode, the protective layer 5 protects the electrooptical materialfrom aluminum atom penetration which leads to degradation of the device.Protective layer 5 can also serve as an insulating layer preventingcurrent from passing through the electrooptical material.

FIG. 4 illustrates an electrooptical device representing a lightmodulator provided with a toroidal cavity employing the longitudinalelectrooptical effect in the layer of the electrooptical material 3.Here, the light beam passes along the axis of cavity 6 through windows 7and 8 constituting a below-cutoff (evanescent) waveguide with respect tothe modulation frequency. The microwave modulation signal is supplied tothe cavity via feedthrough 9. In this electrooptical device, theelectric field 10 is parallel to the light beam. This method oftransmitting light through electrodes is preferred in the microwaverange. The cavity can be considered as the section of a coaxial lineshortened on one end and loaded on the other end with a capacitance ofthe electrooptical anisotropic thin crystal film.

FIG. 5 illustrates an electrooptical device in which a light beampropagates in an electrooptical anisotropic thin crystal film in adirection parallel to the applied electric field 10. In thiselectrooptical device, electrodes 2 are formed on the end portions ofthe electrooptical material layer 3. The light beam is fed in and offthe electrooptical material through optical prisms 11.

FIG. 6 illustrates an electrooptical device analogous to the one shownin FIG. 5, except that electrodes 2 extend from the end portions longthe upper surface of the electrooptical material layer 3, and light beamis fed in and off the electrooptical material via optical waveguides 12having oblique end surfaces.

FIG. 7 illustrates an electrooptical device representing a multilayermodulator cell based on substrate 1. The electrooptical material layers3 are separated by electrodes 2. The voltage is applied to theelectrodes 2 so that the electric fields in the adjacent layers of theelectrooptical material are oriented in the opposite directions. In thisdevice, the angle between the light beam propagation direction and theelectric field vector is either 0 or 180°.

FIG. 8 illustrates an electrooptical device in which the substraterepresents an optical fiber with core 13 and reflective cladding 14.This device performs the function of an optical shutter. The reflectivecladding 14 of the optical fiber is covered by a cylindrical electrodelayer 2, followed by a cylindrical electrooptical material layer 3 andanother electrode layer 2. When an external modulation voltage isapplied to the electrodes 2, the device operates as follows. If theelectrooptical material 3 is characterized by the refractive indexdependent on the voltage applied to the electrodes 2, the modulatedcontrol voltage changes the effective refractive index n_(eff) of thereflective cladding 14 surrounding the fiber core 13 in the region wherethe electrooptical layer 3 and electrodes 2 are situated. When theeffective refractive index n_(eff) is smaller than that of the fibercore, the light beam will deviate from the reflective cladding 14 towardthe core 13 and, hence, will be guided. If the effective refractiveindex n_(eff) is greater than that of the fiber core, the light beamwill pass through the electrooptical material layer 3 withoutreflection. If the electrooptical material 3 is characterized by theabsorption coefficient depending on the external voltage, the light beamis modulated as a result of the guided variation of the opticalabsorption in the region where the electrooptical layer 3 and electrodes2 are situated. The present anisotropic thin crystal film has extremelyhigh anisotropy of both the refractive indices n_(o) and n_(e) and theabsorption coefficients. For this reason, the device as shown in FIG. 8allows the optical modes of different polarization to be also controlledas described.

FIG. 9 illustrates an electrooptical device in which the active(voltage-controlled) system of two cylindrical electrodes 2 andelectrooptical layers 3 is formed in two regions on the optical fiber.This device provides for a deeper optical modulation and can alsoperform the function of an optical shutter.

FIG. 10 illustrates an electrooptical device in which the cylindricalelectrooptical material layer 3 is formed on the surface of reflectivecladding 14 of an optical fiber with the core 13. In this device, twoelectrodes 2 are arranged on the same external cylindrical surface ofthe electrooptical material as depicted in the cross section. The deviceoperates as follows. Variation of the control voltage leads to a changein the effective refractive index n_(eff) of the reflective claddingand/or in the absorption coefficient of the electrooptical layer 3. Thelight beam is modulated due to its reflection from the fiber cladding 14(when n_(eff) is smaller than the refractive index of the fiber core),or due to emission from the fiber (when n_(eff) is greater than therefractive index of the fiber core). The second mechanism of modulationis related to the field-induced variation of the absorption coefficientof the electrooptical material. In this embodiment, the device can beused as an optical shutter. Owing to a high degree of opticalanisotropy, the disclosed device can also be used to control the lightwith respect to polarization.

FIG. 1I illustrates an electrooptical device in which the active(voltage-controlled) system of two electrodes 2 and electrooptical layer3 is formed on a flat surface of the reflective cladding 14 of aD-shaped optical fiber with the core 13 situated closer to the flatinterface.

FIG. 12 illustrates an electrooptical device in which the active(voltage-controlled) system of two electrodes 15 and electroopticallayer 16 is formed in a region of “waist” of the optical fiber. Such awaist can be obtained by local heating and extending of the fiber. Inthe waist region, the fiber has variable cross sections. An advantage ofusing waists in the device is related to the fact that the fiber core 17in such regions is closer to the electrooptical layer 18 formed on thereflective cladding surface. As a result, the light propagating in thecore interacts more strongly with the electrooptical material.

FIG. 13 illustrates an electrooptical device in which the active(voltage-controlled) system of two electrodes 2 and electrooptical layer3 is formed on a flat end surface of a fiber having core 13 andreflective cladding 14. By applying the control voltage betweenelectrodes 2, it is possible either to reflect the beam from the end orto allow the light passing through the electrooptical material. If thevariable electric field changes the absorption coefficient of theelectrooptical material, the light beam is either passed virtuallywithout attenuation, or fully absorbed in the electrooptical layer. Thisdevice can employ a multilayer structure instead of a singleelectrooptical material layer 3. The multilayer structure may consist ofalternating layers with high and low values of the refractive indexand/or with the principal optical axes oriented at an angle from 0 to 90degrees relative to one another. The thickness of the layers can betaken equal to λ/4n, where λ is the light wavelength and n is therefractive index. In general, such multilayer structure can be used as aband-pass or band-stop filter; the low- and high-pass filters can bealso implemented based on such multilayer structures.

FIG. 14 illustrates an electrooptical device based on an optical fiberwith oblique end surface. In this device, the active(voltage-controlled) system of two electrodes 2 and electrooptical layer3 is formed on the flat end surface of a fiber with core 13 andreflective cladding 14. This design of the electrooptical device allowsthe light beam to be extracted from the fiber. As the device shown inFIG. 13, this device can also employ a multilayer structure instead of asingle electrooptical material layer 3, comprising a set of opticallyisotropic and/or anisotropic, electrooptical and/or non-electroopticalmaterials.

FIG. 15 illustrates an electrooptical device operating on the sameprinciple. In this embodiment, the active (voltage-controlled) system oftwo electrodes 2 and electrooptical layer 3 is formed on an oblique endof an optical waveguide 19, for example, of a planar design mounted onsubstrate 1. As the devices shown in FIGS. 13 and 14, this device canalso employ a multilayer structure instead of a single electroopticallayer 3. Moreover, this type of devices is not limited to the geometryillustrated in FIG. 15. For example, the optical waveguide layer may beprovided with a tapered or wedge-shaped end.

FIG. 16 illustrates an electrooptical device based on an optical fiberwith a long-period (100-160 micron) grating 20 formed in the fiber core13. This grating 20 either transforms the fundamental optical mode, orany other guided axial mode with the field concentrated in the paraxialregion, into a peripheral mode propagating in the reflective cladding,or vice versa, converts peripheral modes into the fundamental mode orany other guided axial mode. The long-period grating ensures effectivecoupling of the guided axial modes and the peripheral modes owing to thephase synchronism condition. For this reason, such grating enhances theinteraction of light with the active system of electrodes 2 andelectrooptical layer 3 formed on the surface of reflective cladding 14of the fiber. The electrooptical anisotropic thin crystal filmselectively interacts with the light beam, acting only upon the modescorresponding to the grating period. Since the anisotropic thin crystalfilm has a very high anisotropy, the disclosed device can provide forthe selection of modes with different polarizations. In addition, oncethe thin crystal film is characterized by a strong dependence of theabsorption coefficient on the electric field, this device can alsoperform modulation of light with a selected wavelength with respect toabsorption.

FIG. 17 illustrates an electrooptical device with two long-periodgratings 20 formed in the fiber core 13 and the active system ofelectrodes 2 and electrooptical layer 3 formed in the region between thetwo gratings on the surface of reflective cladding 14 of the fiber.Here, the first long-period grating separates the corresponding modesand transforms them into peripheral modes propagating in the reflectivecladding, while the second long-period grating drives these modes backto the core. The active system of the electrodes and electroopticallayer acts upon the light traveling in the reflective cladding.Similarly to the above example, this device can perform modulation oflight with a selected wavelength with respect to absorption because thethin crystal film is characterized by a strong dependence of theabsorption coefficient on the electric field. Owing to the anisotropy ofthe thin crystal film, this device can also perform modulation of lightwith respect to polarization.

FIG. 18 illustrates an electrooptical device which is a combination ofthe devices as shown in FIGS. 16 and 17.

FIG. 19 illustrates an electrooptical device employing the Bragg grating21 formed in the layer of an electrooptical material 3 by creating thecorresponding profile of the refractive index, which can be achievedthrough variation of the film composition or by laser irradiation. Theelectrooptical layer 3 with the Bragg grating 21 is placed onto the flatpolished surface of a D-shaped optical fiber with core 13 and reflectivecladding 14. The control voltage is applied between the two electrodes 2deposited onto the surface of electrooptical layer 3. Application of thefield modifies the properties of the Bragg grating and hence changes thewavelength of light reflected from the grating.

FIG. 20 illustrates an electrooptical device comprising two single-modeD-shaped optical fibers with cores 13 and reflective claddings 14, whichare rotated with their flat polished surfaces toward each other. Anactive multilayer structure consisting of two electrodes 2 andelectrooptical material 3 is confined between the two optical fibers. Adc and/or ac control voltage is applied between the transparentelectrodes. This device performs the function of an optical switch, theoperation of which is based on the refractive index of theelectrooptical material being dependent on the electric field strength.A field-induced change of the refractive index alters the propagationconstants of modes guided by a planar optical waveguide structure formedby the electrooptical film (waveguide core) and the reflective claddingand the electrode material (reflecting layers). A change in thepropagation constants of the planar waveguide modes alters theconditions of resonance between these modes and the fundamental mode ofthe optical fiber. If the control voltage is such that the initialoptical signal with a given wavelength is out of resonance with allguided modes of the planar optical waveguide formed by theelectrooptical film, the signal is transmitted to the first fiber output22. If the control voltage is such that the initial optical signal witha given wavelength is in resonance with one of the guided modes of theplanar optical waveguide formed by the electrooptical film, the signalis pumped into the planar waveguide and, upon exciting the fundamentalmode of the second fiber, is transmitted to another output 23.

FIG. 21 illustrates an electrooptical device comprising two single-modeD-shaped optical fibers rotated with their flat polished surfaces towardeach other. Confined between the two optical fibers is an activemultilayer structure consisting of two electrodes 2 and electroopticalmaterial layer 3 in which a long-period grating is formed, for example,by laser irradiation. A dc and/or ac control voltage applied between thetransparent electrodes changes the optical parameters of the long-periodgrating. Here, the control of radiation in the visible and near IR range(modulation of the optical signal and/or switching between the twochannels) is due to the long-period grating ensuring phase synchronismbetween the modes of different optical waveguides and thus effectivelycoupling these modes.

The following examples are provided to illustrate the present inventionand not intended to limit the scope of the invention in any way.

EXAMPLE 1

This example illustrates the manufacture of an electroopticalanisotropic thin crystal film of a lyotropic liquid crystal based onsulfided indanthrone organic dye.

The films were prepared from a 9.5% aqueous solution of sulfidedindanthrone capable of forming a hexagonal phase at room temperature.This organic dye occurred in the solution in the form of anisometricsupramolecular complexes, which formed the basis of a crystal structureof the target film. The initial paste was applied onto a clean siliconor glass substrate by means of casting and spreading. Then the colloidsystem was treated to reduce the viscosity for the subsequent alignmentstep. The resulting solution formed a nematic phase or a mixture ofnematic and hexagonal phases with a viscosity reduced from 1780 to 250mPa/s. This preliminary conversion of the colloidal system into a highflow state is a first step before obtaining the high-quality anisotropicthin crystal films of the present invention.

The next operation was the alignment of the kinetic units of thecolloidal system of the lyotropic liquid crystal. The alignment actioncould be provided by various techniques. In this example, the alignmentwas performed using a Meyer wiper No. 4 with a wire wound so as tocontrol a wet layer thickness at 9.5 mm. During the alignment process,the wiper velocity was 13 m/s. Shear stresses arising during the wiperaction upon the layer produced additional decrease in the systemviscosity.

The final stage was drying. The rate of solvent removal was controlledto be sufficiently small not to alter the target structure formed in thepreceding stage. In this example, the drying was performed at roomtemperature and a humidity of 60%.

As a result, anisotropic thin crystal films were obtained with athickness of 0.3-0.4 micron, possessing a high anisotropy of the opticaland electrical properties. The films were characterized by homogeneityof the parameters along the film surface and by good reproducibilityfrom one batch to another. The high crystal structure perfection of thefilms was confirmed by optical methods and by X-ray diffraction.

EXAMPLE 2

This example illustrates the manufacture of electrooptical devices ofthe present invention.

A layer of SnO₂ with a thickness of 0.5 micron was formed by aconventional method. Above this film, an electrooptical anisotropic thincrystal film was formed according to the above described method, whichwas filled by a protective acetate film with a thickness of 10-20 nm.Then aluminum strips of four millimeter wide were deposited in vacuumonto the acetate film surface. Finally, the electrodes were attached andconnected to a source of dc and/or ac control voltage.

EXAMPLE 3

This example illustrates the manufacture of an electrooptical devicebased on a D-shaped optical fiber

A metal film was deposited on the flat surface of a D-shaped opticalfiber. Then a gap of about five to ten micron wide was formed by a laserbeam to divide the metal layer into two electrodes. Finally, anelectrooptical anisotropic thin crystal film was formed above thismultilayer structure according to the above described method.

Of advantages, the electrooptical devices of the present invention iscapable of controlling radiation in the visible and near IR range. Theelectrooptical devices of the invention comprises layers of materialswith variable refractive indices and/or absorption coefficientsdependent on the strength of an applied electric field and/or theelectric field component of visible or IR radiation. The electroopticalmaterials used in the present invention possess a number of usefulproperties including linear variation of the refractive index dependingon the applied field strength (Pockels effect), quadratic variation ofthe refractive index depending on the applied field strength(electrooptical Kerr effect), optical Kerr effect, piezoelectric effect,and electrostriction. The electrooptical devices of the presentinvention can be widely used for controlling amplitude, phase, andfrequency of optical signals, changing the direction of radiation beams,generating short (nanosecond and picosecond) light pulses, and creatingtunable optical filters, electrooptical anisotropic thin crystal opticalmodulators and switches, optical means of protection against excessluminance (radiation limiters), beam deflectors, and other opticaldevices employed, in particular, in fiber optic communication systems.

While the present invention is disclosed by reference to the preferredembodiments and examples detailed above, it is to be understood thatthese embodiments and examples are intended in an illustrative ratherthan limiting sense, as it is contemplated that modifications andcombinations will readily occur to those skilled in the art, whichmodifications and combinations will be within the scope of the inventionand the scope of the appended claims.

1. A method of fabrication of an electrooptical device, comprising:depositing a colloid system of anisometric particles onto at least oneelectrode and/or onto at least one substrate and/or onto at least onelayer of an isotropic or anisotropic material to form at least one layerof an electrooptical material; externally aligning the colloid system toform a preferred alignment of the colloid system particles; drying thecolloid system; and forming at least one electrode and/or at least onelayer of an isotropic or anisotropic material on at least a portion ofthe layer of the electrooptical material.
 2. The method according toclaim 1, wherein the colloid system is either subjected to an externalaction in order to reduce the system viscosity before the externalalignment action, or this alignment action ensuring preferred alignmentof the colloid system is produced in the course of the external actionreducing the system viscosity.
 3. The method according to claim 2,wherein the external action reducing the colloid viscosity is terminatedafter alignment of the system, or an additional external action isproduced in order to restore viscosity of the colloid system at least onthe initial level.
 4. The method according to claim 2, wherein theexternal action upon the colloid system is produced by local and/ortotal heating of the substrate from the side opposite to the layer ofelectrooptical anisotropic material, and/or by local and/or totalheating of the substrate and/or the colloid solution layer from the sameside on which the layer of the electrooptical anisotropic material isformed.
 5. The method according to claim 4, wherein the heating isperformed using radiative and/or resistive heater, and/or an ac electricor magnetic field, and/or a flow of heated liquid and/or gas.
 6. Themethod according to claim 2, wherein the external action upon the systemis produced via a mechanical action upon the colloid solution layerapplied onto a substrate.
 7. The method according to claim 1, whereinthe external alignment action upon the surface of an applied colloidsolution is produced by a directed mechanical motion of at least onealignment device representing a knife and/or cylindrical wiper and/orflat plate or any other instrument oriented parallel to the appliedlayer surface and/or at an angle to this surface, whereby a distancefrom the substrate surface to the edge of the alignment device is presetso as to obtain an anisotropic thin crystal film of a requiredthickness.
 8. The method according to claim 7, wherein a certain reliefis made on the surface of the alignment device.
 9. The method accordingto claim 7, wherein the alignment is performed by heated instrument(s).10. The method according to claim 1, wherein the alignment is performedby application of an external electric field to the system.
 11. Themethod according to claim 1, wherein the alignment is performed byapplication of an external magnetic field to the system.
 12. The methodaccording to claim 1, wherein the alignment is performed by applicationof an external electric and/or magnetic field to the system, withsimultaneous heating.
 13. The method according to claim 1, wherein thealignment is performed by illuminating the system with one or severalcoherent laser beams.
 14. The method according to claim 2, whereinrestoration of the system viscosity at least on the initial level isachieved by terminating the external action reducing the viscosity inthe course of the alignment action.
 15. The method according to claim 1,wherein the drying is performed at room temperature and a humidity ofnot less than 50%.
 16. The method according to claim 1, wherein theanisotropic particles in the colloid system are crystalline.
 17. Themethod according to claim 1, wherein lyotropic liquid crystals areemployed as the colloid system.
 18. The method according to claim 17,wherein the external action is selected so as to provide for a phasetransition in the system.
 19. The method according to claim 1, wherein acolloid system is used in which a disperse phase concentration isselected so as to ensure a thixotropic behavior of the system.
 20. Themethod according to claim 1, wherein an additional aligning action uponthe system after restoration of the initial colloid system viscosity isproduced in the same direction as that in the main alignment stage. 21.The method according to claim 1, wherein the kinetic units of thecolloid system are charged.
 22. The electrooptical anisotropic thincrystal film obtained by the method according to claim 1.